<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>math 对象</title>
	<script type="text/javascript">
		
		var a = 10;
		var b = 20;

		// Math.random 获取0-1的随机数
		// Math.floor 向下取整
		// Math.ceil 向上取整
		var num = Math.floor(Math.random()*(b-a));

		var 
		alert(num);
	</script>
</head>
<body>
	
</body>
</html>